So Amy Lee's vocals but with heavier instruments. Kittie an Arch Enemy have a very different sound imo, Kittie being nu/ alternative metal and Arch enemy being melodic death metal, but I'll see what I can come up with.
Lacuna Coil may be what you're looking for although you've probably already heard of them. Crystal Viper maybe, although I think their vocalist has a more aggressive approach. Definitely try them out though. That's Lacuna Coil and Crystal Viper. I'll try and come up with more later.